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Daisy-Chain two ADS1278EVM boards

Albert Wahba
Prodigy 130 points
Other Parts Discussed in Thread: ADS1278

Hi,

I have an application where I would like to simultaneously sample 16 analog channels, and send the data to a microcontroller through a spi interface. I got two (2) ADS1278EVM boards and one (1) MMB0 Modular EVM motherboard. My intension is to use the MMB0 as a power supply module for both ADS1278EVM cards.

The question that I have is, can I daisy-chain the two ADS1278EVM cards and use the same MMB0 as a common power supply? I noticed that I can cascade both ADS1278EVM cards one on-top of the other as follows: J3A-->J3B, J5A-->J5B, and J9A-->J9B, where all A connectors are located on the bottom board, and all B connectors are located on top board. Placing the two cards on-top of each other will connect the following spi lines in parallel: DIN, DOUT1 which should be daisy-chinned, how can I solve this problem?

Is there is a better way to supply power to the ADS1278EVM boards using a single source power supply, instead of using the MMB0 board?

 

Thanks,

Albert

 

  • 0
    TI__Mastermind 43915 points

    Hi Albert,

    I believe we have been asked this before in the past. Unfortunately, there is no easy way to do this outside of desoldering the specific pin on the bottom connector for DIN and DOUT, pulling it away from the pad and then fly wiring in to set it appropriately.

    Regards,

    Tony Calabria

  • 0 in reply to Tony Calabria
    Prodigy 130 points

    Thanks so much for your prompt reply. Any other pin changes should I keep in mind while doing that?

    Albert

  • 0 in reply to Albert Wahba
    TI__Mastermind 43915 points

    Albert,

    You will want to keep in mind that the ADS1278EVM has a D-Flip-Flop installed for use with the EVM-PDK and MMB0 which will delay the bits by a half clock cycle. U20 on the schematic is the DFF so you will probably want to pull the Dout from the J2 header where you can get the line prior to the flip flop delay. You could also desolder the DFF and hardware the line accordingly. I would also make sure you have the format and mode pins set accordingly using the switches and double check them probing with an Oscope to be sure. Daisy chaining devices will not work with the EVM-PDK, so I imagine that you have some other interface that you are planning to ''fly wire'' into the EVM system.

    Regards,

    Tony

  • 0 in reply to Tony Calabria
    Prodigy 130 points

    Hi Tony,

     

    Thanks for your reply...

    I noticed that DFF in the circuit diagram, and I also saw lots of posts about that. So, I agree with you, I will be connecting directly to DOUT1 before the DFF, and I will be connecting an external uController to the spi interface directly. The MMB0 board is just used as a power supply.

     

    Thanks,

  • 0 in reply to Albert Wahba
    Prodigy 130 points

    Hi Tony,

     

    I did the changes to the boards to allow DOUT1 from one board to the DIN in the second board, and mounted both boards to the MMB0 board; the MMB0 board is just used as a power supply, as I removed both J5B and J9B.

    I tried each board separately on the MMB0, and they works fine, but the problem is that when I connect both boards together and mount them on the MMB0 board, they don't work, and the reason seems to be that the MMB0 power supply can't handle both ADS1289EVM boards.

     

    Am I doing anything wrong, or the MMB0 board can't supply enough power to both ADS1278EVM boards?

     

    If the MMB0 can't handle both boards, is there is an easy way to supply power to the ADS1278 boards? Do I have to use more than one power supply?

     

  • 0 in reply to Albert Wahba
    TI__Mastermind 43915 points

    Hi Albert,

    Take a look at the ADS1278EVM User's Guide. You can use alternate supplies rather than the charge pumps to power the on board op amps. On the MMB0, remove the J12 jumper and use the J14 header to apply 5V, +/-10V to power the board instead of the wallwart. You will also need to change some of the jumpers on the ADS1278EVM board to use external supplies rather than the on board charge pumps.

    -Tony

  • 0 in reply to Tony Calabria
    Prodigy 130 points

    Hi Tony,

     

    Thanks for your reply. I was able to get it to work by connecting the first ADS1278EVM to the MMB0 board till I get the power supply ready, then add the second ADS1278EVM board. I don't know if there is a way around that or not.

    The reason why I am trying to stick with one power supply is that the new design will be mounted on a rotating shaft, and I have limited number of slip-ring connections.

     

    Thanks,

    Albert